My amp has a PPIMV. When I dime the controls and max the PPIMV my HT Fuse (500mA) blows after 10 minutes of playing. However when I run the PPIMV at 50% the amp can be played endlessly.
I have this layout. http://www.ceriatone.com/images/layoutPic/marshallLayout/Plexi50LeadCeriatone.jpg
With a multimeter the reading at HT1 is 433 dcv.
If that reading is fine, could the problem be that the amp is biased too hot?